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Water vapor mystery puzzles astronomers

The James Webb Space Telescope has detected water vapor in a red dwarf star system, but its source is still an open question.

(CN) — Researchers utilizing the James Webb Space Telescope announced Monday that they have detected signs of water vapor in a nearby star system.

But they're not exactly sure where it's coming from.

In a study first drafted in April for the Astrophysical Journal Letters, the scientists said one possibility is that the water is present in the outer layers of the star itself — a red dwarf known as Wolf 437. Red dwarfs are the most common form of star in the universe, and as their name implies are relatively cool and small. Astronomers estimate Wolf 437, located 26 light years away from Earth in the constellation Virgo, has about a third the mass of the sun and only shines about 1% as brightly.

Water vapor sometimes collects on the surface of our own star, in transient regions of decreased temperature called sunspots. These cool regions are short-lived manifestations of chaotic magnetic fields writhing within the solar interior, and on a chilly red dwarf like Wolf 437, much more water vapor could potentially accumulate in its own sunspots.

The more interesting possibility is that the water vapor originated in the atmosphere of the rocky planet gj 486b, which closely orbits Wolf 437. That gj 486b may even have an atmosphere is noteworthy, given the planet's close orbit around its host star and the harsh conditions it endures. It's about 30% larger than Earth and three times as massive, circles Wolf 437 at only about 2% the average distance Earth orbits the sun, and like Mercury, is likely tidally locked to its star. This means one side of the planet always faces Wolf 437 while the other is cast in an eternal night, with an estimated planetwide average surface temperature of 800 degrees Fahrenheit.

Red dwarfs like Wolf 437 are also infamously moody. Their luminosity can fluctuate wildly, dimming for months only to suddenly flash twice as bright as normal in a matter of minutes. They can also eject waves of charged particles into space which, over time, can crumple planetary magnetic fields and dissolve planetary atmospheres. The closer the planet to the star, the more intense the stellar tantrums it endures.

In theses conditions, researchers said it would be extraordinary for a rocky planet like gj 486b to retain an atmosphere —much less atmospheric water vapor. It would likely indicate the planet has high levels of volcanic activity to replenish atmospheric chemicals lost to the solar winds.

“We see a signal, and it’s almost certainly due to water. But we can't tell yet if that water is part of the planet's atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” said lead study author Sarah Moran of the University of Arizona in a press release on Monday.

The confusion over whether Wolf 437 or gj 486b is the source of the water vapor comes from how scientists observed the exoplanet. Using the James Webb Telescope, they watched Wolf 437 as gj 486b passed in front of it. If the planet has an atmosphere, the red dwarf's light would pass through it en route to Earth. Chemicals in that atmosphere would refract the light into distinct wavelengths, leaving a telltale spectroscopic fingerprint. The same phenomenon is observable on Earth: our sky is blue because of how atmospheric oxygen and nitrogen scatter the sun's light.

But confirming the presence of an atmosphere on an exoplanet 26 light years away is no east feat, even for the Webb Telescope's advanced infrared cameras. It's just as likely, researchers said, that the telescope was simply detecting water-laden sunspots on the surface of Wolf 437 as gj 486b passed in front of it.

“We didn't observe evidence of the planet crossing any starspots during the transits. But that doesn't mean that there aren't spots elsewhere on the star," said Ryan MacDonald of the University of Michigan in Ann Arbor, another of the study’s authors, in a statement. "And that's exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere.”

More observations will be necessary to determine the exact source of the water vapor, researchers said. Unfortunately, even if the vapor proves to originate in gj 486b's atmosphere, the planet is still too close to its star to host life as we know it. But finding any atmosphere could still change scientists' understanding of rocky planets beyond our solar system.

“Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science," said Kevin Stevenson of the Johns Hopkins University Applied Physics Laboratory, one of the scientists studying gj 486b, in a statement. "But we must be careful and make sure that the star is not the culprit.”

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Categories / Environment, Science

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